Chemical sensors can be used to analyze a wide variety of environmental and bodily gases, aerosols and fluids for properties of interest.
For example, exhaled breath condensate (EBC) is widely known to be a diagnostically important bodily fluid that can be safely collected. In particular, the breath from deep within the lungs (alveolar gas) is in equilibrium with the blood, and therefore the concentrations of molecules present in the breath is highly correlated with those found in the blood at any given time. Analysis of molecules and pH value in exhaled breath condensate or incondensable gases is a promising method that can provide information on the metabolic state of the human body, including certain signs of cancer, respiratory disease, lungs, intestine, liver and kidney function, and other internal organs. Several different analysis methods including gas chromatography (GC), chemiluminescence, selected ion flow tube (SIFT), and mass spectroscopy (MS) have been used to measure different exhaled biomarkers, including hydrogen peroxide, nitrogen oxide, aldehydes, carbon dioxide, hydrogen, and ammonia. However, these methods show vary significantly in sensitivity.
In another example, chloride ion detection can be accomplished. In the body, chlorine exists primarily as the chloride ion. The chloride ion is an essential mineral for humans, and is maintained to a total body chloride balance in body fluids such as serum, blood, urine, exhaled breath condensate etc., by the kidneys. Chloride can be found in the body mainly in the extracellular fluid along with sodium. Some of body chloride is found inside the cells, with the highest amounts within the red blood cells. As one of the mineral electrolytes, chloride works closely with sodium and water to help the distribution of body fluids. Chloride is easily absorbed from the small intestine. It is eliminated through the kidneys, which can also retain chloride as part of their finely controlled regulation of acid-base balance. Chloride is also found along with sodium in perspiration. Variations in the chloride ion concentration in serum may serve as an index of renal diseases, adrenalism, and pneumonia. Thus, the measurement of this parameter is clinically important. Several analytical methods, such as colorimetry, ion-selective electrodes, activation analysis, X-ray fluorescence spectrometry, and ion chromatography, have been used for the analysis of chlorine in various samples. However, these methods are not portable and require expensive instrumentation. Accordingly, an accurate and fast determination of the inorganic ion content of various aqueous samples at low detection limits is of great interest.
Yet another example of sensing application using body fluid is detecting breast cancer with saliva. The mortality rate in breast cancer patients can be reduced by increasing the frequency of screening. The overwhelming majority of patients are screened for breast cancer by mammography. This procedure involves a high cost to the patient. Moreover, the use of invasive radiation limits the frequency of screening. Recent evidence suggests that salivary testing for markers of breast cancer may be used in conjunction with mammography. Saliva based diagnostics for the protein c-erbB-2, a prognostic breast marker assayed in tissue biopsies of women diagnosed with malignant tumors, has shown tremendous potential. Soluble fragments of the c-erbB-2 oncogene and the cancer antigen 15-3 were found to be significantly higher in the saliva of women who had breast cancer than in those patients with benign tumors. Another recent study concluded that epidermal growth factor (EGF) is a promising marker in saliva for breast cancer detection.
Pilot studies indicate that the saliva test is both sensitive and reliable and is potentially useful in initial detection and follow-up screening for breast cancer. However, currently saliva samples are typically obtained from a patient in a dentist's office then sent to a testing lab; it typically takes a few days to get the test results.
To fully realize the potentials of sensors for environmental, health related, chemical and biomedical applications, technologies are needed that will enable easy, sensitive, and specific detection of chemical or biomolecules at home or elsewhere. It is also desirable that a testing device allows concomitant wireless data transmission into preprogrammed destinations, such as transmitting breast cancer testing results to a doctor or clinic. If inexpensive technologies that can detect and wirelessly transmit testing results for environmental, health related, chemical and biomedical applications can be developed, early diagnosis of cancers or disease can significantly lower mortality and the cost of health care. Real-time wireless remote sensing for chemicals in the environment may reduce the incidence of disasters by alert to a chemical hazard.